Defining a Quality Rebuilt Torque Converter

DEFINING a Quality Rebuilt Torque Converter ,
By Steve Jaussaud , Torque Converter Rebuilder's Association What makes a rebuilt torque converter a quality unit? That's easy, you say: A quality rebuilt torque converter is one that works correctly when you install it and doesn't cause your customer to return to your transmission shop with a problem.

OK, we can all agree on that. But how do you really define it? What measurable criteria can be used to determine if a converter is good or poor quality?

The membership of ATRA is asking the Torque Converter Rebuilder's Association to, as an industry trade group, work towards developing this measurable criteria. This article is the first in a series of articles that will discuss how we can better define torque converter quality. TCRA believes that the first step in developing measurable criteria for the industry is to lay out some basic terminology. This way, with the benefit of all parties using a common language, issues can be intelligently analyzed and discussed. If torque converter rebuilders and transmission rebuilders don't at least start off with a basic understanding of a common glossary of terms, cooperation between the two will just be that much more difficult.

The two terms presented in this initial article are Overall Height and Endplay . These are features of the torque converter that can be measured from the outside of the unit. As a transmission rebuilder, you do not have the ability to analyze and look inside every converter that you use. Understanding the concepts and having the necessary tools to analyze theses aspects of a converter can at least give you a fighting chance when trying to determine if you have a quality unit. As you will see in future articles in this series, some concepts are easily defined, while some concepts are elusive and, by their nature, difficult to pin down.

Overall Height:

  The overall height of a torque converter is a simple measurement, but there are things that you have to pay attention to. The measurement is taken from the surface of the converter that sits flush against the flexplate (typically a 'pad' or 'lug') to the leading edge of the impeller hub. Overall height (often referred to as 'stack height') is not from the tip of the pilot to the tip of the hub. See figure 1. On converters that use 'studs' in lieu of 'pads' to fasten to the flexplate (E4OD / 4R100 units, for example), you must measure from the base of the stud, not the tip of the stud. Additionally, a converter should be placed on a true, flat surface and measured with a precision height gauge. Measurements taken on dented steel bench with a construction tape measurer will not give you valid data. Especially when you consider that a unit with an overall height that is 'out of spec' by only a few thousandths of an inch can cause problems. And remember, correct overall converter height does not guarantee that you have the right converter. For example, remember the A4LD converters that were in the old Merkurs, the one with the short pilot? That converter has the same overall height as a regular A4LD converter. Again, it is important to remember that if you are measuring overall converter stack height in this manner, pilot length has no bearing on the overall height of the converter . That Merkur A4LD converter has the same spline count, stall speed rating, overall diameter, bolt circle diameter, pilot diameter, as well as the same overall height as a standard A4LD converter, but they are not interchangeable, only because of the pilot length.

And how does a converter rebuilder know what the correct overall height should even be? There are a number of charts that have floated around the industry for a number of years showing overall average heights. From experience, I can tell you that some of these charts can contain both correct and incorrect information. But without OEM drawings of each individual OE part number, it is difficult to determine the exact parameters and allowable range of each application. Generally, converter rebuilders get their overall height ranges from precision measurement of virgin cores. Having a good height spec on an E4OD converter is no big thing, even for a small one or two man torque converter rebuilding operation. Everybody sees plenty of those. But having a valid height spec on a late model oddball unit that somebody has already cut open during a previous rebuild is a different story.

Torque Converter Endplay:

Everybody knows that when you pick up a converter and shake it, components inside the unit rattle back and forth. Nobody panics when these parts shift back and forth, because we all know that the torque converter must have internal clearance or end play. Elements in a torque converter need to rotate separately and freely from each other, and endplay gives them just enough room to do that. But how much is just enough? And how do you correctly measure torque converter clearance? How do you reliably 'set' the clearance during the rebuild process? Do you need to set clutch (pack) clearance as well as overall unit clearance, just as in a transmission? The answers to these questions, as with seemingly all things automotive, depend on application.

How much clearance is the correct amount? Some early AODE units came from Ford with as much as .050" overall endplay. The internal components you might replace in that AODE converter (and the design of those components) will dictate the amount of clearance that you would set that same AODE at when rebuilding it. I have seen some late model Honda units have as little as .004". Anybody remember the old Mercedes fluid couplers with the extra small 1.100" diameter impeller hubs? It is not uncommon to find clearances of .150" or more in those units. As you can see, there is not a 'one size fits all' number for proper internal clearance. And unlike measuring the overall height from a previously unrebuilt core, measuring the internal end play from a 'virgin' core will not always give you accurate OE design criteria, only because you do not know if the clearance measurement you get has been impacted by the failure of any internal thrust surfaces. If you are trying to get valid endplay clearance data from core measurement, you need to first measure for endplay, then cut the unit open and inspect for any damage or wear that could make your measurement invalid.

How do you correctly measure torque converter clearance? Torque converter clearance can be measured in a variety of ways. Some methods are easier and more accurate than others. Reaching down into a converter with snap ring pliers and 'lifting' components, for example, may tell you if a converter has internal clearance, but it is not an accurate way to precisely determine how much clearance is in the converter. There are several tools on the market today that will accurately measure torque converter clearance. Although it is a bit pricey, the quickest and easiest tool out there to adapt to a wide variety of applications seems to be the TCRS Endplay Gauge. (FIG 2).

How do you reliably set torque converter clearance during the rebuild process? In actuality, it does not really matter how you set it, as long as it comes out correct. Some rebuilders use removeable shims, while some use sophisticated fixture devices that not only align the components prior to and during the weld, but preset endplay as well. I only bring this up, because there are arguably advantages and disadvantages to both methods. People that favor using a fixture to preset clearance will tell you that shims can be left in the unit, can fracture and leave debris in the unit, and/or the process of shim removal can damage internal components. Rebuilders that use removeable shims will argue that presetting the endplay is not precise enough, because of the variable nature of shrinkage that occurs during the welding process. As stated, it really doesn't matter how it's done, as long as you get the proper results.

Do you need to set torque converter clutch clearance separately from overall unit clearance, just as in a transmission? In a word, yes. However, how you set clutch clearance depends on – all together now – application . There are some late model Mercedes 722.6 torque converters that have an actual multiple disc clutch pack, complete with pressure plate and snap ring. There are also late model ZF converters that have a 'captive clutch', where the damper and separate clutch plate are 'staked' into place. Transmission rebuilders can relate to setting clearances in clutch packs that are designed like this, tranny shops deal with clutch pack clearance on a routine basis. When rebuilding both of these types of units, you absolutely have to pay attention to clutch clearance, separately from endplay clearance. But what about setting separate clutch clearance on units that don't have a 'captive clutch'? On these units, setting overall endplay will accommodate clutch clearance as well. But a good converter builder will still pay attention to the available travel of the clutch plate. Converter rebuilders often need to cut thin sections of material from either the clutch surface on the front cover, or from the clutch plate itself. Cutting excessive material from either of these surfaces can cause problems due to too much clutch clearance. Resulting symptoms are more prevalent in some applications over others. Additionally, some lock up converters maintain a thrust surface between the turbine hub and the front cover, while some do not. Ignoring the interal clearance of these components can build problems into units. The point of bringing all of this to light is that clutch clearance is a separate issue from overall clearance, and clutch clearance cannot typically be measured from the outside of a finished torque converter.

In conclusion, it is evident that considerable documentation, planning and control must be part of a good converter remanufacturing operation. And a good converter remanufacturer is always looking for ways to improve communications with you, the transmission rebuilder. If we can all have a better understanding of the terms and definitions used in converter production, we will all benefit in the long run. Look for the next articles in this series for the presentation of such concepts as: Impeller Hub Diameter and Finish, Pilot Diameter and Condition, and Torque Converter Run Out.